Radiofrequency transformer

ABSTRACT

A radiofrequency transformer having a metal outer case of a given cross section for enclosing coils therein and has a magnetic shield comprising four rods of a magnetic material each interposed and held between a respective corner of the outer case and a corresponding corner of a rigid inner case.

United States Patent- [72] Inventor Kyuuernon Funakl [56] References Cited simm'l'kem FOREIGN PATENTS 295,502 1928 Great Britain 336/84 [22] Filed Sept. 25,1970

660,474 l95l Great Bnta|n..... 336/84 1 m 086 l/l969 0 H3 '13- 336/84 [73] Assignee Tolto Klbushlkl Keisha ma Tokyo-to, Japan Primary Examiner-Thomas J. Kozma [32] Priority Oct. 13,1969 Anorneys- Robert E. Burns and Emmanuel .I. Lobato [33] Japan [3|] 44197356 [54] RADIOFREQUENCY TRANSFORMER 7chlmsannwing ABSTRACT: A radiofrequency transformer having a metal [52] 0.8. CI. 336/84, outer case of a given cross section for enclosing coils therein 174/35 TS, 336/233 and has a magnetic shield comprising four rods of a magnetic [51] Int. Cl. H0" 15/04 material each interposed and held between a respective [50] Field of Search 336/84, corner of the outer case and a corresponding corner of a rigid '(IIIIIIIIIIIIIIIIII.

inner case.

PATENTED on: 1 19?:

FIG.

I I I I I I I I I I I I I n RADIOFREQUENCY TRANSFORMER BACKGROUND OF THE INVENTION This invention relates generally to radiofrequency transformers such as, for example, double-tuned IF transfonners and more particularly to a new and advanced radiofrequency transformer.

In general, transformers of this class have a metal case and internal coils enclosed therein. If the case and coils are close together, the quality factor or Q characteristic of the coils will be lowered. Accordingly, it has been the conventional practice to line the inner wall surface of the metal case with a magnetic shield structure of sheet form generally produced from a rubber or synthetic resin containing a magnetic material such as iron oxide powder. This magnetic shield structure is secured to the metal case by means of an adhesive.

However, securing this magnetic shield sheet accurately and positively onto the inner side of a small metal case has been difficult. Furthermore, the sheet thus secured tends to separate from the metal case because of temperature variations and changes with the passing of time. For this reason and partly for other reasons, deviations in the inductance, characteristics, and other characteristics of the coils easily occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide radiofrequency transformers of simple construction and low manufacturing cost in which the above described difficulties are overcome.

It has been found that this object can be achieved by providing, in a radiofrequency transformer of the type referred to above, a magnetic shield comprising at least two bars of magnetic material interposed and held between the metal outer case and a rigid inner case with orientation directions parallel to the axis of the coils or the central bobbin.

The nature principle, details and utility of the invention will be more clearly apparent from the following detailed description with respect to a preferred embodiment of the invention when read in conjunction with the accompanying drawing, in which like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is an elevation view in vertical section, illustrating one example of a radiofrequency transformer according to the invention;

FIG. 2 is a cross section view of the transformer shown in FIG. I; and

FIG. 3 is a perspective view of the inner case of the transformer shown in FIGS. 1 and 2.

DETAILED DESCRIPTION Referring to the drawing, a radiofrequency transformer, according to the invention illustrated therein has a central bobbin I mounted on a base 2 and supporting coils 3. The base 2 is of substantially rectangular or square shape in plan view and provided with terminal pins 5. The entire bobbin 1 and coils 3 are fully enclosed within a metal outer case 4 having a substantially rectangular or square cross section with rounded comers and fitted at its base end onto the periphery of the base 2.

A feature of the invention is that at least two bars of magnetic material are disposed near or in contact with the inner wall surface of the outer case. In the example illustrated, the magnetic material is in the form of four round bars or rod 6 disposed in the corner parts of the outer case 4 and held against the inner wall surface thereof by a rigid inner case 8 having a rectangular or square cross section with corners 7 which are recessed or arcuately concave inwardly, and are shaped to fit snugly against and partly around the periphery of res ective rods 6.

he magnetic material 6 in rod form may be a rigld material such as a ferrite, or it may be a flexible material such a synthetic resin or rubber caused to contain a magnetic material such iron oxide powder with uniform distribution.

Furthermore, the arrangement of this magnetic material is not limited to that of four rods 6 in respective corners of the metal case but may be one in which two rods are disposed in diagonally opposite comers.

It has been found that, while the magnetic rods 6 are disposed at only the comers of the metal case in accordance with the invention, such an arrangement afiords ample magnetic shielding effect in actual practice.

Moreover, the magnetic material can be installed in ac cordance with the invention merely by placing it between the metal outer case 4 and the inner case 8, e.g., between the comer of the outer case 4 and the concave comer 7 of the inner'case 8, and there is no necessity of securing a magnetic shielding structure over the entire surface of the case as heretofore. Accordingly, the fabrication of the radiofrequency transformer is facilitated. Furthermore, since the magnetic material is held securely against the metal outer case by the riding inner case, the inductance and Q characteristics of the coils can be stabilized in a permanent manner.

Moreover, since the magnetic material, such as rods 6 in the above described example, can be produced with high uniformity and homogeneity, deviations of characteristics of each class of transformer can be minimized.

While, in the foregoing example, the metal outer case 4, and therefore the inner case 8, have substantially square cross sections, it will be apparent the shape of these cross sections need not be so limited. Examples of other possible cross-sectional shapes are a rectangle other than a square, a diamond, a circle, an ellipse, an oval, polygons such as a hexagon and and octagon, and closed figures with crenated and corrugated peripheries.

I claim:

1. In a radiofrequency transformer having a metal outer case for shielding coils enclosed therein and aligned on an axis, the improved combination therewith of a rigid inner case, a magnetic shield comprising at least two bars of magnetic material interposed and held between the outer case and the rigid inner case and orientated in directions parallel to said axis.

2. The combination as claimed in claim 1 in which the outer case has rounded outwardly corners and arcuate concave corners recessed inwardly, the bars of magnetic material comprising four round rods each held between a respective corner of the outer case and a corresponding concave comer of the inner case.

3. The combination as claimed in claim 1 in which the magnetic material is a rigid magnetic material.

4. The combination as claimed in claim 2 in which the magnetic material is a rigid magnetic material.

5. The combination as claimed in claim I in which the magnetic material is a flexible material containing particles of a magnetic material with uniform distribution.

6. The combination as claimed in claim 2 in which the magnetic material is a flexible material containing particles of a magnetic material with uniform distribution.

7. The combination as claimed in claim 1 in which the outer case has a substantially square cross. section with corners rounded outwardly, and the inner case has a corresponding square cross section with arcuate concave corners recessed inwardly, the bars of magnetic material comprising two rods held between respective rounded corners of the outer case and corresponding concave corners of the inner case at diagonally opposite comers of the outer and inner cases.

l i t Il 

1. In a radiofrequency transformer having a metal outer case for shielding coils enclosed therein and aligned on an axis, the improved combination therewith of a rigid inner case, a magnetic shield comprising at least two bars of magnetic material interposed and held between the outer case and the rigid inner case and orientated in directions parallel to said axis.
 2. The combination as claimed in claim 1 in which the outer case has rounded outwardly corners and arcuate concave corners recessed inwardly, the bars of magnetic material comprising four round rods each held between a respective corner of the outer case and a corresponding concave corner of the inner case.
 3. The combination as claimed in claim 1 in which the magnetic material is a rigid magnetic material.
 4. The combination as claimed in claim 2 in which the magnetic material is a rigid magnetic material.
 5. The combination as claimed in claim 1 in which the magnetic material is a flexible material containing particles of a magnetic material with uniform distribution.
 6. The combination as claimed in claim 2 in which the magnetic material is a flexible material containing particles of a magnetic material with uniform distribution.
 7. The combination as claimed in claim 1 in which the outer case has a substantially square cross section with corners rounded outwardly, and the inner case has a corresponding square cross section with arcuate concave corners recessed inwardly, the bars of magnetic material comprising two rods held between respective rounded corners of the outer case and corresponding concave corners of the inner case at diagonally opposite corners of the outer and inNer cases. 